Solvent extraction process



y 1965 J. w. GEMMELL 3,193,489

SOLVENT EXTRACTION PROCESS Filed Sept. 13, 1962 rop so CRUDE CHARGE 36 CAT. l0 CRACKING 33 '7" 25 RECOVERY E5 502 CRACKED CHARGE 2| PRODUCT?) PRODUCT n 35 37 FRACTIONATION 34 7 q 8 s0 CYCLE '5 U RECOVERY OIL GAS OIL E CHARGE} CAT. PRODUCT 5 I9 CRACKING FRACTIONATION Z '6 L18 22 23 CYCLE 36/ on.

RECOVERY EXTRACT OIL INVENTOR. J.W. GEM MELL W WW A 7' TORNEKS United States Patent 3,193,489 SULVENT EXTRAGTION PROCESS John W. Gemmell, Idaho Falls, Idaho, assignor to Phillips Petroleum Company, a corporation of Delaware Filed Sept. 13, 1962, Ser. No. 223,357 6 Claims. (Cl. 208-80) This invention relates to a solvent extraction process wherein aromatic hydrocarbons are removed from a hydrocarbon mixture by means of a selective solvent. In one aspect this invention relates to a method for operating a solvent extraction process so as to remove intermediate aromatics therefrom, thus reducing the intermediate aromatic content of the ratlinate and of the extract. In another aspect this invention relates to a solvent extraction process operated in conjunction with a plurality of catalytic hydrocarbon cracking steps operated at different levels of conversion and to a method for removing the intermediate aromatic oils from the solvent extraction step to provide a portion of the feed to a catalytic cracking step which is practiced at a relatively low conversion level.

It is known to crack hydrocarbon fluids catalytically to increase the quantity and quality of the gasoline or motor fuel product. In such operations a refractory heavy product is produced, for which there is little demand and therefore this heavy product is usually returned to the cracking operation. It has been proposed to solvent extract this heavy recycle oil so as to remove aromatic hydrocarbons which are carbon formers and gas formers and to recycle the rafiinate to the cracking operation. The extract from the solvent extraction step constitutes a preferred feed stock for the manufacture of carbon black by the furnace process and the demand for such aromatic extract has increased substantially over the past few years. It has also been proposed to employ two or more catalytic cracking zones, wherein feed stocks containing different concentrations of contaminating metals are separately cracked, to solvent extract the heavier oil from the cracking zone which treats the feed stock containing the least amount of contaminants, to pass this raflinate to the cracking zone wherein the feed stock contains the greatest amount of contaminants and to pass the extract oil to a carbon black process.

It is an object of the invention to provide a process which will remove a side stream rich in intermediate aromatic hydrocarbons from a solvent extraction step so as to produce a raflinate and an extract each of which has a reduced intermediate aromatic hydrocarbon content. It is also an object of this invention to provide a process which will reduce the amount of intermediate aromatic hydrocarbons in the raflinate of a solvent extraction step, which raflinate is passed to a catalytic cracking step operating under severe cracking conditions. A further object is to increase the aromatic hydrocarbon production of a refinery operation wherein a plurality of catalytic cracking steps are operated at different conversion and temperature levels. A still further object of the invention is to provide a solvent extraction apparatus wherein a stream intermediate the rafiinate and the extract can be recovered from the solvent extraction apparatus. Other objects and advantages of the invention will be apparent to one skilled in the art upon study of this disclosure including the drawing and the detail description of the invention.

The drawing is a diagrammatic flow plan of a preferred embodiment of the invention.

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In the catalytic cracking of a hydrocarbon stream there is produced a mixture of liquid hydrocarbons comprising parafiinic hydrocarbons, aromatic hydrocarbons, and intermediate aromatic hydrocarbons. The paraffinic hydrocarbons are the straight and branch chain hydrocarbons and the aromatic hydrocarbons are the benzene ring hydrocarbons and short side-chain derivatives of the benzene ring hydrocarbons. The intermediate aromatic hydrocarbons are the aromatic hydrocarbons having long side chains such as the alkyl aromatic hydrocarbons. The solvent extraction process which is selective to aromatic hydrocarbons will be also somewhat selective to the intermediate aromatic hydrocarbons or the alkyl aromatic hydrocarbons but to a considerably lesser degree. Thus, in a conventional solvent extraction process a portion of the intermediate aromatic hydrocarbons will be contained in the extract phase and another portion of the intermediate aromatic hydrocarbons will be contained in the raflfinate phase. It the rafiinate phase containing a substantial quantity of intermediate aromatic hydrocarbons is passed to a catalytic cracking step operated at high temperature and conversion level, a substantial portion "of the aromatic producing, intermediate aromatic compounds will be destroyed at the expense of the aromatic hydrocarbon production of the operation.

According to the present invention there is provided a solvent extraction process having provisions for removing a raffiuate stream which is rich in intermediate aromatic hydrocarbons. Also according to the present invention means are provided to pass the raflinate stream, which is rich in intermediate aromatic hydrocarbons, to a catalytic cracking step conducted at low temperature and low conversion level whereby the intermediate aromatic hydrocarbon is cracked to produce a parafiinic hydrocarbon and an aromatic hydrocarbon, thus increasing the production of both parafiinic hydrocarbons and aromatic hydrocarbons. A mild catalytic cracking step, i.e., catalytic cracking step conducted at low conversion level and low temperature, is herein defined as a catalytic cracking step operated at a temperature in the range of 870 to 900 and at a conversion level of about 30 to about 40 percent conversion. A severe catalytic cracking step, i.e., a catalytic cracking step conducted at high temperature and high conversion level, is herein defined as a catalytic cracking step operated at a temperature of about 905 to 930 and a conversion level of about 50 to percent conversion. The intermediate aromatic hydrocarbon hereinbefore referred to is defined as a hydrocarbon containing at least one benzene ring and an alkyl side chain containing at least 3 carbon atoms. The alkyl side chain can be a straight chain or a branched chain hydrocarbon. Representative examples of intermediate aromatic hydrocarbons include normal propyl benzene; normal butyl benzene; isobutyl benzene; normal amyl benzene; methyl ethyl benzene; normal heptyl benzene; normal octyl benzene; and the like.

Referring now to the drawing, a hydrocarbon feed stream comprising topped crude, pitch, and/or other hydrocarbon fluids containing relatively large amounts of metal compound contaminants or coke and gas-forming components are introduced to a first catalytic cracking zone 11 via conduit 10. The hydrocarbon efiluent from catalytic cracking zone 11 is passed via conduit 12 to a product fractionation zone 13 wherein a gasoline fraction and other products are removed via conduit 14. Hydrocarbons heavier than the desired products, comprising cycle oils, are passed via conduits 15 and 16 to solvent extraction zone 17.

areaeso Gas, oiland other distillates which are low in metal oxide content are introduced to' a second catalytic crackas is introduced into the upper portion of solventextraction zone or tower 17 via conduit 25 so as to pass downwardly in countercurrent relationship with respect to the cycle oils introduced into the extraction zone via conduit 16. Hydrocarbon is the continuous phasein the upper portion of the tower, above feed conduit'l, and solvent is the continuous phase in the lower portion of the tower 17. An extract comprising solvent and arematic hydrocarbons is removed from the bottomof the extraction zone 17 via conduit 26 and is passed to S0 recovery zone 27 wherein S0 is separated from the arcmatic extract oil and is passed via conduit 28 for reuse in the process. The aromatic extract oil is recovered via conduit 29.

A raffinate stream comprising paraiiinic hydrocarbons and solvent is removed from the top of the solvent extraction zone 17 via conduit 31, separated from S0 in S0 recovery zone 32 and passed via conduit 21 to catalytic cracking zone 13. S0 is removed from S0 recovery .zone 32 via conduit 33 for reuse in the process. 7

A stream rich in intermediate aromatics is removed from solvent extraction zone 17 via conduit 34, separated from S0 in 80 recovery zone 35 and passed via conduit 36 to catalytic cracking zone 11; from S0 recovery zone 35 via conduit 37 for reuse in the process.

A solvent extraction operation for separation of aro- .matic and parafiinic hydrocarbon will normally be carried out in a vertical column or tower, with or without contacting means such as bubble cap trays, perforated trays, solid packing, and the like. The solvent such as liquid S0 phenol, furfural, and the like is introduced into the upper portion of the column and the hydrocarbon feed is introduced into the lower portion of the column. This is the normal procedure when the solvent is more dence than the feed and when countercurrent operation is practiced. The parafiinic'raflinite is withdrawn from the top of the column and the aromatic extract is withdrawn from the bottom of the column.

According to the practice of the invention a stream is withdrawn from the extraction column at a point intermediate the feed inlet and rafiinate outlet and at a point where the concentration of intermediate aromatics is relatively great as compared to the concentration of arcmatics. where the concentration of intermediate aromatics is greatest for any given set of operating conditions.

It is believed that the rcgenerated,'relatively pure, and cool solvent dissolves the hydrocarbon feed as the feed enters the column. The solvent, however, being selective to aromatics rejects the paraifinic hydrocarbon in favor of the intermediate aromatics and rejects the intermediate aromatics in favor of the aromatics. It is possible in theory, and even perhaps in practice, to recover a paraifinic rafiinate which is substantially free of aromatics and to recover an aromatic extract which is substantially free from parafiins; however, the intermediates having no place S0 is removed.

Samples withdrawn from the column will show In a system such as illustrated in the drawing the first catalytic cracking zone (11) is operated at relatively low conversion and the second catalytic cracking zone (18) is operated at relatively high conversion as shown in the following Table I.

Table l First Second Solvent Cracking Cracking Extrac- Zone (11) Zone (18) tion Zone Pressure, p.si g

(To 12 10 107 T .(Botttorn). r 134 1 4 emplera are, 95 910 3? Conversion; percent ..I 34. 4 54.1 Liquid S0 bbl./day-. 13,500

The increase in the quantity of aromatic extract oil produced in the practice of the invention is shown in the following Table 11 wherein the numbered column headings refer to streams according to the drawing.

Table II' PRIOR ART Stream No 15 1 16 21 29 Barrels/Dayn 9,487 12,513 17, 060 4,940

PRACTICE or INVENTION Stream N0. 15 10 e 21 29 30 Barrels/Day 7,200 9,300 5,000 0,100 4,800 BMOU 50.0 7 40.0 12.0 93.0 25.0

1 Total of l5+16=22,000. 2 Total of l5+16=16,500. 3 Bureau of Mines Correlation Index.

The above tabulation reveals that even though the invention is practiced with a smaller feed stream wherein fewer barrels per day of materials are processed that the quantity of aromatic extract oil is increased. Although not shown in the above tabulation, the amount of product I in the gasoline range, and lighter, is also increased.

to go will appear in both the raffinate and the extract in a. 1

ratio which will be determined by operating conditions, solvent properties, andother variables. Removal of a stream rich'in intermediates will reduce the amount of intermediates in each of the raflinate and the extract.

Reasonable variations and modifications arepossible within the scope of this disclosure without departing from the spirit and scope of the invention. e

That which is claimed is: i

1. in a process for treatinghydrocarbon fluids wherein a hydrocarbon stream having a high metal contaminant content is catalytically cracked in a first cracking zone operating under mild cracking conditions and a hydrocarbon stream having a low metal contaminant content is catalytically cracked in a second cracking zone operating under severe cracking conditions, the improvement comprising recovering cracked products from said oracle ing zones; passing the cycle oils produced in said cracking zones to a solvent extraction step for separation of paraffinic' from aromatic materials; removing a raffinate stream, substantially denuded of aromatics, from said solvent extraction step and passing same to, said second cracking zone; recovering an aromatic hydrocarbon extract stream from said solvent extraction step as a product of the process;.and removing a stream containing a substantial quantity of intermediate aromatic hydromediate aromatic content of the raflinate and the extract which comprises removing a stream of liquid from the extraction process at the locus of greatest concentration of intermediate aromatic.

4. The process of claim 3 wherein the aromatics are recovered as a product of the process and the intermediate aromatics are passed to a process for converting said intermediate aromatics to parafiins and aromatics.

5. In a process for treating hydrocarbon fluids comprising catalytically cracking a first hydrocarbon stream having a high metal contaminant content in a first cracking zone at a conversion level below about 40; catalytically cracking a second hydrocarbon stream having a low metal contaminant content in a second cracking zone at a conversion level above about 50; recovering cracked products from the efiluent streams of said first and second cracking zones as products of the process; passing remainder of the efliuent streams, heavier than the products, to a solvent extraction zone, extracting aromatics from the remainder of the eflluent streams as an additional product of the process; passing the rafiinate from said solvent extraction zone to said second cracking zone; the improvement comprising passing a stream, removed from said solvent extraction zone at the locus of highest concentration of alkyl aromatics having an alkyl chain of from 3 to 12 carbon atoms, attached, to said first cracking zone.

6. In a system for treating hydrocarbon fluids comprising a first catalytic cracker, a second catalytic cracker, hydrocarbon separation means for recovering hydrocarbon products from the efiiuent materials from said catalytic crackers, the combination therewith of a solvent extraction column; means to pass liquid solvent to the upper portion of said extraction column; means to pass catalytic cracker effiuent materials from which products have been recovered to the lower portion, of said extraction column; means to pass paratfinic raflinate to said first catalytic cracker; means to recover aromatic extract from said extraction column; and means to remove material intermediate said raflinate' and said extract from said extraction column and to pass same to said second catalytic cracker.

References Cited by the Examiner UNITED STATES PATENTS 2,702,782 2/55 Little 20896 2,852,442 9/58 Moy 208-96 2,941,936 6/60 Harper 208-96 ALPHONSO D. SULLIVAN, Primary Examiner. 

1. IN A PROCESS FOR TREATING HYDROCARBON FLUIDS WHEREIN A HYDROCARBON STREAM HAVING A HIGH METAL CONTAMINANT CONTENT IS CATALYTICALLY CRACKED IN A FIRST CRACKING ZONE OPERATING UNDER HAVING A LOW METAL CONTAMINANT CONTENT IS CATALYTICALLY CRACKED IN A SECOND CRACKING ZONE OPERATING UNDER SEVERE CRACKING CONDITIONS, THE IMPROVEMENT COMPRISING RECOVERING CRACKED PRODUCTS FROM SAID CRACKING ZONES; PASSING THE CYCLE OILS PRODUCED IN SAID CRACKING ZONES TO A SOLVENT EXTRACTION STEP FOR SEPARATION OF PARAFFINIC FROM AROMATIC MATERIALS; REMOVING A RAFFINATE STREAM, SUBSTANTIALLY DENUDED OF AROMATICS, FROM SAID SOLVENT EXTRACTION STEP AND PASSING SAME TO SAID SECOND CRACKING ZONE; RECOVERING AN AROMATIC HYDROCARBON EXTRACT STREAM FROM SAID SOLVENT EXTRACTION STEP AS A PRODUCT OF THE PROCESS; AND REMOVING A STREAM CONTAINING A SUBSTANTIAL QUANTITY OF INTERMEDIATE AROMATIC HYDROCARBONS FROM SAID SOLVENT EXTRACTION STEP AND PASSING SAME TO SAID FIRST CRACKING ZONE. 